Published 16.09.2026 · Reading time 12 min · By the Voldt® product team

A granny charger is a portable EV charging cable with an ordinary three-pin plug at one end, a Type 2 connector at the other and a control box in between. You need an earthed 13 A socket in good condition and nothing else. The number that matters is 10 A: that is 2.3 kW, or roughly 6 to 8 miles of range for every hour the car is plugged in.

Below you will find what the name means, why a 13 A plug is normally run at 10 A, how many hours and pounds a charge takes for cars actually sold in the UK, how a granny charger compares with a 16 A socket or a wallbox, and the rules Electrical Safety First and the IET Wiring Regulations set for charging from a household socket.

A portable charger in practice: the control box hangs from an ordinary wall socket, with the cable running to the car's charge port.

Key points

Question	Short answer
What is a granny charger?	A Mode 2 portable charging cable: 13 A three-pin plug, control box, Type 2 connector. Every EV with a Type 2 inlet can use one. See the technical card.
How fast does it charge?	2.3 kW at 10 A, about 6 to 8 miles of range per hour, or 60 to 80 miles from a 10-hour night. See the model table.
Why not use the full 13 A?	A BS 1363 socket is rated for 13 A, not for 13 A without pause for ten hours. 10 A is the trade default for sustained charging; 13 A belongs on an EV-marked socket on its own circuit. See section 2.
What does a charge cost?	About £6 for a 10-hour session at 10 A at the October to December 2026 price cap of 26.32p/kWh. See the cost table.
Is it safe?	Yes, on a sound, earthed socket on a lightly loaded circuit. Electrical Safety First advises against extension leads and against daisy-chaining them in all circumstances. See safe use.
Granny charger or wallbox?	Under about 30 miles a day, a granny charger covers it. Above 40, a 7 kW wallbox. See the comparison table.

What is a granny charger?

A granny charger is a Mode 2 charging cable: a 13 A three-pin plug, an in-cable control box and a Type 2 connector for the car, delivering 1.8 to 2.8 kW depending on the current you set.

The name is slang, and the usual explanation is that it is the cable you take when you visit your grandmother, whose house has sockets but no charge point. The trade uses drier words for the same thing: Mode 2 charging cable, portable EV charger, 3-pin EV charger, EVSE. Under IEC 61851-1, Mode 2 means charging from a standard household socket with the protection built into the cable instead of into the wall. Whether your car can use one is covered in is my EV suitable for charging from a normal outlet; every EV with a Type 2 inlet can.

Portable chargers also exist with a blue 16 A industrial plug for campsites, marinas and dedicated sockets. This article is about the three-pin version only: the one that plugs into the socket you already have and needs nothing installed.

That protection sits in the control box, the plastic block a short way down the cable from the plug. It is an in-cable control and protection device, or IC-CPD, to IEC 62752. Before any power flows it checks that the socket is earthed. While charging it watches for residual current, including DC fault current, and switches off the moment it sees any. And it tells the car how much current it may draw. The car's onboard charger does the conversion to DC and fills the battery; the box only controls and protects.

The current setting is the one thing you actively choose. A fixed unit sits at one value, usually 10 A. An adjustable unit lets you step between 8 and 13 A to suit the socket in front of you. The plug on the Voldt® granny charger also has a temperature sensor: if the plug gets too hot, the charger drops the current. Section 2 explains why the top setting is the one you will use least.

Technical card: Voldt® 3-pin granny charger

Why does a 13 A plug give you 10 A of charging?

A BS 1363 socket is rated to supply 13 A, not to supply 13 A without pause for ten hours: 10 A is the current the trade has settled on for sustained charging from an ordinary socket, and 13 A belongs on a socket built and wired for it.

A kettle draws about 13 A for three minutes. A tumble dryer draws around 10 A and cycles its heater on and off. EV charging is different: the load is constant, for as long as the car takes. Constant current warms the plug pins, the socket contacts and the terminal screws behind the faceplate. A socket in good condition takes it. A 20-year-old outdoor socket with slightly sprung contacts runs warmer, and the warmth speeds up the wear that caused it.

Electrical Safety First tells drivers to have their wiring checked before charging from a 13 A socket, because older wiring may not cope with the demand of charging overnight. No UK law sets a maximum current for charging from a socket; the 10 A convention comes from the trade and the cable makers, and it leaves a margin below the socket's rating for the reason above.

Two things move the line. The first is the socket. BS 1363-2 covers socket-outlets marked "EV", designed for sustained 13 A load. The second is the circuit behind it. A charging point installed for the purpose falls under Section 722 of BS 7671, the IET Wiring Regulations: its own circuit from the consumer unit and a 30 mA RCD that also detects DC fault current. An EV-marked socket on a Section 722 circuit is where the 13 A setting makes sense. Anywhere else, leave the unit at 10 A.

How long does a granny charger take, and what does it cost?

At 10 A about 2 kW reaches the battery, so a 10-hour night adds roughly 20 kWh, 60 to 80 miles of range, and costs about £6 at the October to December 2026 price cap.

The socket supplies 2.3 kW at 10 A. The onboard charger and the battery turn part of that into heat, proportionally more at low power than at high, so around 2.0 kW reaches the cells; the table assumes that, and 2.5 kW at the 13 A setting. Most drivers charge from about 20% to 80% rather than empty to full, so that is the span shown. Battery figures are the manufacturers' nominal capacities; what charging speed do I need for my EV has the same sums for wallboxes and public chargers.

Model (UK spec)	Battery, kWh	20 to 80% at 10 A	20 to 80% at 13 A	10-hour night at 10 A adds
Dacia Spring	26.8	8 h	6.5 h	20% to full
Renault 5 E-Tech 52 kWh	52	15.5 h	12.5 h	38%
BYD Dolphin	60.4	18 h	14.5 h	33%
MG4 Long Range	64	19 h	15.5 h	31%
Tesla Model Y Long Range (approx.)	75	22.5 h	18 h	27%
Kia EV3 Long Range	81.4	24.5 h	19.5 h	25%

In practice: a 60 kWh car will not get a full charge from a granny charger in one night, and does not need one. Thirty miles a day uses 8 to 10 kWh, which the socket puts back in four to five hours. Tesla does not publish its battery capacities; the 75 kWh figure is the commonly quoted estimate.

Session	Energy drawn from the socket	Cost at 26.32p/kWh
1 hour at 10 A	2.3 kWh	£0.61
10-hour night at 10 A	23 kWh	£6.05
10-hour night at 13 A	28 kWh	£7.37
20 to 80% on a 60 kWh battery (about 41 kWh from the socket)	41 kWh	£10.79

The rate is the Ofgem price cap for 1 October to 31 December 2026, Great Britain average for Direct Debit customers, with no VAT on electricity in that period; the 54.83p daily standing charge is paid whether or not you charge. Per mile that works out at roughly 8 to 9p. An EV tariff changes the sum: at an off-peak rate of 8p, the same 23 kWh night costs £1.84. For the comparison with the kerbside, see why public kWh prices vary so much.

Granny charger, 16 A socket or wallbox: which do you need?

Under about 30 miles a day, a granny charger at 10 A on a sound socket does the job; above 40 miles, or whenever you need a full battery by morning, a 7 kW wallbox is the answer, and a 16 A industrial socket sits usefully between the two.

The middle column is the one UK drivers overlook. A blue 16 A IEC 60309 "commando" socket on its own circuit gives 3.7 kW, 60% more than a granny charger at 10 A, for the cost of a socket and a circuit, and the same 16 A portable unit works at campsites and marinas. The single-phase versus three-phase question behind the wallbox column is in 1-phase vs 3-phase charging, 16 A vs 32 A; the wallbox decision itself is in mobile Type 2 charger or fixed wallbox. A socketed wallbox also needs its own Type 2 charging cable.

For the "best granny charger" question, these are the spec sheet lines that decide it:

Your situation, our advice

Charging stops or will not start: causes and fixes

Most interruptions at a household socket come down to heat, a shared circuit or a missing earth; the table pairs each symptom with its fix.

Control box shows an earth fault and will not start+

Likely cause: The socket has no earth, or the earth connection is broken

Fix: Try another socket; have the first one checked by an electrician. Never bypass the earth check

Charging stops after an hour or two and the breaker has tripped+

Likely cause: The circuit is shared with a heavy appliance, or the MCB is old

Fix: Move to a socket on a lighter circuit, drop to 8 A, and ask an electrician about a dedicated socket

Charging stops during the night and the RCD has tripped+

Likely cause: Moisture in the plug or socket, or a fault in another appliance on the same RCD

Fix: Dry and inspect plug and socket; use a weatherproof outdoor socket; if it repeats, have the installation tested

Car shows a scheduled or delayed charge and does not start+

Likely cause: Departure time or off-peak schedule set in the car

Fix: Charging menu > charge now (or clear the schedule), then reconnect the cable

Charger drops to 8 A though you set 10 or 13 A+

Likely cause: The plug temperature sensor has cut the current because the plug was getting too hot

Fix: Let the plug cool and check the socket; a socket that keeps heating the plug needs replacing

Plug or socket hot to the touch+

Likely cause: Worn socket contacts or a loose terminal behind the faceplate

Fix: Stop. Replace the socket before charging from it again

Frequently asked questions about granny chargers

Is the cable that came with my car a granny charger?+

Usually, yes. Most manufacturers supply a Mode 2 cable with a three-pin plug, often fixed at 10 A and sometimes at 8 A. A separate adjustable unit lets you leave one at home, keep one in the car, and pick the current for the socket in front of you.

Does the fuse in the plug protect the socket?+

No. The 13 A BS 1362 fuse in a UK plug protects the cable and the appliance against fault current; it does nothing about a socket slowly overheating at a steady 10 to 13 A. A blown fuse points to a fault: replace it like for like and find the cause before charging again.

What about heavy-duty extension leads sold as "EV-rated"?+

Electrical Safety First advises against charging through extension leads; where it gives any guidance at all, it is for an outdoor-rated lead, fully uncoiled, never daisy-chained. Our advice is stricter: an extension lead adds a second plug-and-socket joint carrying 10 A for hours, and the money is better spent towards a properly installed outdoor socket.

Can I leave it charging overnight and unattended?+

Yes, at 10 A on a sound, earthed socket on a lightly loaded circuit, with the plug and socket protected from rain. Check plug and socket temperature during your first few sessions; after that, treat it like any other appliance you leave running.

Does slow charging harm the battery?+

No. Slow AC charging generates little heat in the battery; heat and cell stress come mainly from rapid DC charging, and several manufacturers' manuals recommend AC charging for everyday use and DC for journeys.

Does it work in rain and frost?+

The control box and the Type 2 connector are IP67 and take rain without trouble. The socket is the weak point: use a weatherproof outdoor socket with a cover that closes over the plug, and keep the plug out of standing water. Frost does not affect charging; a cable frozen into a puddle is a different problem.

Can I use my UK granny charger in France or Spain?+

No. The BS 1363 plug does not fit continental sockets, and a travel adaptor is not built for 10 A over several hours. On the continent you need a Mode 2 unit with a CEE 7/7 Schuko-style plug, sold on our European stores. Our travel guide, travelling with Voldt® in the UK, covers what to pack.

Do I need a smart charger to use a cheap EV tariff?+

No. Off-peak tariffs bill by the clock, and your car's own charging schedule makes the granny charger start and stop inside the window. What you do need is a smart meter, which the supplier requires for the tariff.